Synchronous dynamic random access memory

ABSTRACT

A synchronous DRAM has cell arrays arranged in matrix, divided into banks accessed asynchronously, and n bit I/O buses for transferring data among the cell arrays. In the DRAM, the banks are divided into m blocks, the n-bit I/O buses located between adjacent banks, is used for time sharing between adjacent banks in common, the n bit I/O buses, used for time sharing between adjacent banks in common, are grouped into n/m-bit I/O buses, every n/m bits for each block of m blocks of bank, and in each block in each bank, data input/output are carried out between the n/m-bit I/O buses and data bus lines in each block. A synchronous DRAM includes a first and second internal clock systems for controlling a burst data transfer in which a string of burst data being transferred in synchronism with an external clock signal, when one of the internal clock systems is driven, the burst data transfer is commenced immediately by the selected internal clock system.

This is a continuation of application Ser. No. 08/997/967, filed Dec.24, 1997, now U.S. Pat. No. 6,018,491, which was a continuation ofapplication Ser. No. 08/718,786 filed Sep. 24, 1996, now U.S. Pat. No.5,715,211, which was a divisional application of Ser. No. 08/310,945,filed on Sep. 23, 1994, now issued as U.S. Pat. No. 5,596,541 of HarukiToda (inventor currently of record in prior application), whichapplications are hereby incorporate by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a synchronous Dynamic Random AccessMemory (DRAM) for burst read/write operations.

2. Description of the Prior Art

FIG. 1 shows a conventional dynamic RAM (DRAM) with a conventional basicarchitectural configuration. FIG. 2 shows a detailed drawing of theconventional DRAM shown in FIG. 1.

In the conventional basic architectural configuration of the dynamic RAM(DRAM), as shown in FIG. 1, data read out of a memory cell selected by aword line is transferred to a sense amplifier (S/A) via a bit line.

A pair of data items amplified by the S/A are read out to an outputbuffer 104 through a pair of FETs 101 (shown in FIG. 2) through whichthe pair of data items are controlled by a signal on a column selectline CSL.

In the conventional basic architectural configuration of the DRAM shownin FIGS. 1 and 2, we will describe one of architectural configurationsof a conventional synchronous DRAM (SDRAM) below.

FIG. 3 shows a path of the synchronous data read/write operations forthe input and output of one unit of data. These operations will now bebriefly explained.

During the output of one string of serial data, when the head address ofthe data in the string is provided, two adjacent CSLs corresponding tocolumn select lines CSL1 and CSL2 are selected, and four items of datafrom memory cells are read out through four pairs of DB lines. This is a2-bit prefetch system whereby data read out of two columns within twoclock cycles simultaneously is transferred serially, and two pairs of DBlines are selected to coincide with serial access addressing from thefour pairs of DB lines. This selection is performed by a DB selector.The data on the two pairs of selected DB lines transferred to two pairsof RWD lines RWD1 and RWD2. Data in the first two cycles on the twopairs of RWD lines are stored into registers R1 and R2, and data in thenext two cycles are stored into registers R3 and R4.

In this write operation of the registers R1 to R4, the sequence forstoring the data form RWD lines RWD1 and RWD2 in the registers R1 to R4is determined by RWD switches RWDS1 and RWDS2.

The data passing through these switches RWDS1 and RWDS2 is stored inaccess sequence into the registers R1 to R4 by register transfer gatesRTG1 and RTG2 which open alternately every two cycles to provide highspeed data output.

The RWD switches 1, 2 and the register transfer gates RTG1 and RTG2, asshown in FIG. 3, are made up of gates of FETs. The data stored in theregisters R1, R4, for example, as shown in FIG. 4, is read out to theoutput buffer 104.

FIG. 5 shows a timing chart of the data transfer state in this data readoperation described above. In FIG. 5, the data transfer state isillustrated under the condition that the burst length is 8 and thenumber of latency is 3 counted after address is determined or latched.

In FIG. 5, the operational state of each of the configurational elementsshown in FIG. 3 is illustrated. These will now be explained in order.

First, in a clock cycle (CLK), a Column Address Strobe (/CAS) isswitched from high to the low, the head address of one string of burstdata is set, and access is commenced. After the head address isdetermined, according to the addressing sequence of the burst dataaccess, an internal address is produced for every two cycles and anaccess operation is carried out at the rise of levels of every twocolumn select lines CSL.

When the column select line CSL rises, the DB line pair immediatelyenters to a busy state. When the data has been kept satisfactorily onthe DB line pair, using the DB selector, data from two pairs infour-pair DB lines is transferred to the RWD line pair, and the RWDlines enter to the busy state every two cycles.

When data is kept sufficiently on the RWD lines, the data is stored intothe register by the operation of the registered transfer gates RTG1,RTG2 and one of the RWD switches RWD1 and RWD2.

In this data store operation, the RWD switches 1 or 2 are suitablyselected by addressing for the burst data and turned ON, normally theregister transfer gates 1 and 2 are alternately ON, and the data isstored in the register.

When the respective register transfer gates RTG1 and RTG2 are turned ON,the contents of the register are immediately rewritten and data istransferred serially from an OUTPUT which enters the busy state.

While these burst data transfer are controlled, after the access for theburst data transfer is completed, the clock cycle for commencing a newburst transfer access is restricted because the internal operation isoperated in two clock cycles. In other words, a time restriction isproduced so that a new access is not commenced from an optional cycleafter the burst data transfer is completed. When a new burst datatransfer access is commenced from an optional cycle after the previousburst data transfer is completed, it is necessary to temporarily resetthe control of the clock period and commence the new burst data transferafter two clock cycles.

For this reason, a data burst completion signal is generated internallyat a time when the burst data transfer access is completed and when itbecomes unnecessary to control the burst data transfer access. Thecontrol system is reset from the clock cycle in which the data burstcompletion signal is generated. This clock cycle is designated by thereference number CLK9 shown in FIG. 5.

Because if the reset is not completed it is not possible to commence anew burst data transfer cycle and a time period of several tens of ns isrequired for the reset, the setting of a new starting address for a newburst data transfer occurs from a clock cycle 11. For this reason, it isnot possible to set a new burst access in clock cycles CLK9 and CLK10.Accordingly, the output of a new burst data transfer is not possibleafter the thick dotted line in FIG. 5, so that data output of the newburst data transfer is only possible after the thin dotted line, whichis disadvantageous in high speed burst data transfer.

As can be seen from the foregoing description, the reset operationdescribed above is required in a conventional synchronous DRAM duringthe transfer for a burst data string. Because this reset operation takesa comparatively long time, it is very troublesome to transfer burst datacontinuously at high speed.

In addition, in a conventional synchronous DRAM, the data transfersystem for cell arrays of multibank architectural configuration is notarranged in an optimum manner, necessitating an increase in the area ofthe chip.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is, with dueconsideration to the drawbacks of such conventional synchronous DRAM, toprovide a synchronous DRAM wherein the arrangement of cell arrays with amultibank architectural configuration and a data transfer system isoptimized and/or high speed burst data transfer is achieved.

In accordance with one aspect of the present invention, there isprovided a synchronous Dynamic Random Access Memory (DRAM) comprising:

a plurality of cell arrays, each of which contains cells, arranged inrows and columns, and being divided into a plurality of banks whichbeing accessed asynchronously; and

a plurality of n bit I/O buses for the simultaneous input and output ofn bits of data among said plurality of cell arrays,

wherein said each bank is divided into m blocks (m is a positiveinteger) with a plurality of said cell arrays,

the n-bit I/O buses (n is a positive integer), located between adjacentbanks, is used for time sharing between adjacent banks in common,

said n bit I/O buses, used for time sharing between adjacent banks incommon, are grouped into n/m bit I/O buses, every n/m bits for eachblock of m blocks of bank, and

in each block in each bank, data input/output are carried out betweensaid n/m-bit I/O buses and data bus lines in each bank.

In the synchronous DRAM above, said n/m-bit I/O buses are locatedbetween adjacent banks.

The synchronous DRAM above, further comprising drive means for drivingsaid cell arrays,

wherein a predetermined numbers of said Data Bus (DB) lines are locatedbetween adjacent cell arrays, said DB lines are used for time sharing incommon by said adjacent cell arrays, and said adjacent cell arrays aredriven alternately under the control of said drive means.

In the synchronous DRAM above, N=8 and m=2, a 8 bit I/O bus is providedin common between said adjacent banks, each bank is divided into 2blocks, and each block uses a 4 bit I/O bus in said 8 I/O bus.

In the synchronous DRAM above, n=8 and m=4, a 8 bit I/O bus is providedin common between said adjacent banks, each bank is divided into 4blocks, and each block uses a 2 bit I/O bus in said 8 bit I/O bus.

In the synchronous DRAM above, further comprises I/O buffers, eachcorresponds to each of said I/O buses, and said I/O buffer is locatedadjacent to an I/O pad corresponding to said I/O buffer.

In accordance with another aspect of the present invention, there isprovided a synchronous DRAM comprising:

a first internal clock system and a second internal clock system forcontrolling a burst data transfer in which a string of burst data beingtransferred in synchronism with an external block signal, when one ofsaid internal clock systems being driven, the burst data transfer iscommenced immediately by said selected internal clock system,

wherein when the transfer of a string of burst data is completed underthe control of the first internal clock system or when a burst interruptsignal for interrupting the transfer of the string of burst data isinput, the first internal clock system enters to a reset state, and thesecond internal clock system is driven to control the transfer of astring of a next burst data.

In the synchronous DRAM above, further comprises a first internal clocksystem and a second internal clock system for controlling a burst datatransfer in which a string of burst data being transferred insynchronism with an external clock signal, when one of said internalclock systems being driven, the burst data transfer is commencedimmediately by said selected internal clock system,

wherein when the transfer of a string of burst data is completed underthe control of the first internal clock system or when a burst interruptsignal for interrupting the transfer of the string of burst data isreceived, the first internal clock system enters to a reset state, andthe second internal clock system is driven to control the transfer of astring of a next burst data.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features, and advantages of the presentinvention will become more apparent from the following description ofthe preferred embodiments taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a basic configuration drawing for a conventional DRAM.

FIG. 2 is a diagram showing one part of the configuration of theconventional DRAM shown in FIG. 1.

FIG. 3 is a diagram showing one part of the configuration relating to aburst data transfer for a conventional synchronous DRAM.

FIG. 4 is a diagram showing one part of the configuration of thesynchronous DRAM shown in FIG. 3.

FIG. 5 is a timing chart for the burst data transfer operation of thestructure of the synchronous DRAM shown in FIG. 3.

FIG. 6 is a configuration drawing for the first embodiment of asynchronous DRAM of the present invention.

FIG. 7 is a block diagram showing the relationship between cell arraysand data buses in a cell array pair shown in FIG. 6.

FIG. 8 is a diagram showing the relationship between data transfer pathsand banks shown in FIG. 6.

FIG. 9 is a block diagram showing a driver means for driving cell arraysincorporated in the synchronous DAM of the present invention.

FIG. 10 is another configuration drawing for the first embodiment of asynchronous DRAM of the present invention.

FIG. 11 is a configuration drawing for the relationship between I/Obuses and I/O pads in a synchronous DRAM of the present invention.

FIG. 12 is a configuration drawing of two internal clock systems in asynchronous DRAM as a second embodiment of the present invention.

FIG. 13 is a diagram specifically showing one part of the configurationof the second embodiment illustrated in FIG. 12.

FIG. 14 is a diagram specifically showing one part of the configurationof the embodiment illustrated in FIG. 11.

FIG. 15 is an operation timing chart for the structure shown in FIG. 14.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Other features of this invention will become apparent in the course ofthe following description of exemplary embodiments which are given forillustration of the invention and are not intended to be limitingthereof.

Embodiments of the present invention will now be explained withreference to the drawings.

FIG. 6 is an architectural configuration diagram for a first preferredembodiment of a synchronous Dynamic Random Access Memory (synchronousDRAM) of the present invention.

The first embodiment shown in FIG. 6 can basically be considered as asynchronous DRAM with a 64 Mega-bits (64 Mb) structural configuration.The 64 Mb synchronous DRAM shown comprises four banks each of which is4096 Rows×512 Columns×8 I/Os (2×4 I/Os).

Each bank includes two blocks, for example, block1 and block 2 in thebank 1. Each block comprises eight cell array pairs 63, each of the cellarray pair is 1 M bits. In further detail, as shown in FIG. 7, each 1 Mbcell array pair 63 consists of two cell arrays 71 and 72, each of 1024Columns×512 Rows with sense amplifiers (S/As) incorporated between thetwo cell array 71 and 72. Each of the blocks in each bank has a data bus61 for every four I/Os. In this manner, a bank is divided into twoblocks with each half corresponding to half of I/Os, so that eight I/Oscan be accommodated with a bus for four I/Os, namely for four blocks.This configuration provides a reduction in the chip area because thearea of I/O buses 61 is half of the area of the conventional synchronousDRAM shown in FIG. 1.

In addition, when driving the cell arrays, for example, in the case ofthe bank 1, the 1 Mb cell array pairs 63 indicated by the slanted linesare driven, and each cell array pair 63 uses every two I/Os. Each I/Obus 61 is formed from four I/Os and is provided in common between theadjacent two banks, for example between the bank 1 and the bank 2 orbetween the bank 3 and the bank 4. This is because data cannot betransferred to two banks at the same time from the specifications of thesynchronous DRAM.

Next, the architectural configuration of the data transfer path betweenthe cell array and the I/O bus will be explained.

FIG. 7 is a block diagram showing the detailed configuration of one cellarray pair 63 (slanted line section) as shown in FIG. 6.

In FIG. 7, cell arrays 71, 72, and 73 are made up of 1024 Columns×512Rows. Sense amplifiers (S/As) 74 are used in common on the two sides ofthe cell arrays 71 and 72 and perform a sensing operation for bit lines76 of the cell array 71 or 72 which is driven. The S/A 74 aligned on thetwo sides of the selected driven cell array, for example, cell array 72carries out a sensing operation on a bit line of that cell array.

Four pairs of data bus lines DB11, DB12, DB13, DB14 are located betweenthe cell arrays 71 and 72, and four pairs of data bus lines DB21, DB22,DB23, DB24 are provided between the cell arrays 72 and 73. For example,two pairs in the data bus lines DB11, DB12, DB13, and DB14 are selectedby a DB selector 75. Data is transferred in the same manner as explainedin FIG. 3.

Not shown in FIG. 7, for the connection of bit lines 76 represented by adotted line and each S/A 74, switch circuits which are cut off as annon-driven cell array is provided between each S/A 74 and each bit line76.

The bit lines 76 in one cell array are arranged into the right directionand the left direction every two to form different I/Os. As shown inFIG. 7, column select lines CSL1 and CLS2 indicated two adjacent columnselector lines selected simultaneously at each clock cycle. By thecolumn select lines CLS1 and CLS2, the two DB lines in the four pair ofI/Os which are on the both sides of the cell array 72 are connected tothe S/A 4 at a time.

Next, the connection relationship between the I/O1 to I/O4 RWD linesconsisting of the I/O buses are shown in FIG. 8. FIG. 8 shows the part62 enclosed by the dotted line shown in FIG. 6.

FIG. 8 shows the I/O1 RWD lines to the I/O4 RWD line which are thecommon I/Os for the bank 1 and the bank 2. The cell arrays 63 as theslanted line section in the bank 1 is selectively driven. The enlargedconfiguration of the cell arrays 63 are shown in detail. Every other oneof the two cell arrays are driven. For example, the cell array 71 and 73shown by the slanted lines are driven. The driven DB selectors 81 to 84are also indicated by the slanted lines and connected to I/O1 RWD lineto I/O4 RWD line in sequence to the half of the blocks shown in FIG. 8forming the bank 1. Also, the RWD lines for the I/Os 5, 6, 7, 8 areconnected to other half of the blocks for the banks not shown in FIG. 8.

The DB lines are used in common at the both sides of the cell arrays 71to 74 so that if this type of data transfer path is provided it ispossible to assign the address of I/O to each cell array effectively bydriving every other one of the cell arrays.

FIG. 9 is a block diagram showing a driver means 90 for driving the cellarrays 71 to 74 incorporated in the synchronous DRAM of the firstembodiment of the present invention. In FIG. 9, two cell arrays 71 and73 are driven under the control of the driver means 90. The data fromthe cell array 71 are transferred to the I/O1 and I/O2 RWD lines throughthe DB selectors 81 and 82. The data from the cell array 73 aretransferred to the I/O3 and I/O4 RWD lines through the DB selectors 83and 84 (indicated by the slanted lines). Thus, the DB lines are used incommon by the adjacent cell arrays. For example, the DB lines connectedto the DB selector 82 are used for the cell array 71 and the cell array72 in common under time-sharing.

Accordingly, by means of the cell arrays and the data transfer pathswith this architectural configuration of the first embodiment of thepresent invention described above in detail, it is possible to form alarge volume synchronous DRAM can be formed because the increase of thesystem area caused by the data transmission paths can be held to aminimum. Specifically, the architectural configuration of thesynchronous DRAM as this embodiment is that each bank is divided intotwo blocks and the I/O RWD lines assigned in two parts, and the databuses which can be used for time-sharing are separated partially and thedata transfer paths in the data buses which can be used for timesharingbetween the banks an the like is provided in common with the cellarrays, the banks, and the like.

In the first embodiment described above, one bank is divided into two.However, as shown in FIG. 10 for example, one bank may also be dividedinto four blocks BLOCK1 to BLOCK4 and 2 bit I/O buses can be used forthe respective blocks.

Also, in the configuration arrangement shown in FIG. 6, if an I/O buffer(omitted from FIGS. 6 and 11) corresponding to the respective I/O buses61, as shown in FIG. 11, is formed in a layout region 106 (designated bythe dotted line) for pads adjacent to an I/O pad (omitted from FIG. 11),the wiring path between the I/O buffer and the I/O pad is short, and itis possible to provide a reduction in the chip area.

FIG. 12 is a view of a second embodiment of the present invention and isa block diagram of a clock system for controlling the internaloperation, showing the architecture for alleviating the limitations ofthe reset explained in the conventional example of an internal clock forcontrolling the data transfer.

The heavy lines in FIG. 12 show one signal path. When one series ofoperations is completed for this system, reset and switching signals aretransferred to each block as shown by the dotted lines.

An external clock signal CLK is transferred through a switch S1 to theinternal clock system 1 which generates a signal for controlling theoutput from the registers R1 to R4 shown in FIG. 3. The internal clocksystem 1 receives an external signal/CAS to generate an internal clocksignal for control from the external clock signal CLK. The internalclock signal drives a burst control section 117 for controlling a burstdata access through a switch W1.

When one string of burst access is completed under the control of theburst control section 117 or when a burst interrupt signal providedexternally is received which halts the burst access in progress, an ENDsignal is transferred to a block ES118 which generates a reset andswitching signal from the burst control section 117. The block ES118outputs a signal R1 or a signal R2 alternately each time the END signalis received. FIG. 13 shows the case where then signal R1 rises. At thistime the signal R2 drops. As a result, the switch S1 if OFF, the switchS2 is ON, the internal clock system 1 enters to a reset state and theinternal clock system 2 is in the standby state.

Next, when the /CAS signal is received, the internal clock system 2 canoperate at any time, in accordance with the external clock signal CLK.Also, the switch S1 is OFF and the switch S2 is ON. As a result, thecontrol of the next burst data transfer operation is carried out fromthe internal clock system 2.

In this manner, the next burst data operation can be performed by usinganother internal clock system without delaying the completion of thereset of the internal clock system used up to this point, therefore theconventional type of restrictions are not produced. In other word, thetime restriction that a new access is commenced from an optional cycleafter the previous burst data transfer is completed is not produced inthe second embodiment.

The switches S1, S2, W1, W2, the internal clock systems 1 and 2, and theburst control section 117 shown in FIG. 12 are structured, for example,as shown in FIG. 13.

The switches S1, S2, W1, W2 are formed from a complementary FET. Theinternal block systems 1 and 2 comprise a shift register 120 whichgenerates a control signal for controlling sequentially a transfer gate129 which controls the output of data from registers R1 to R4, and atransfer gate 129 which controls the output of data from registers R1 toR4, and a transfer gate 121 for selecting control signals for theinternal clock system 1 and the internal clock system 2 which aregenerated by shift registers 120 based on the switching signals R1 or R2and then providing one of them to the transfer gates 129.

The burst control section 117 comprises a counter 122 for counting thelength of one string of a burst data transfer to know the completion ofthe burst data transfer, and an OR gate 123 which transfer an END signalfrom the output of the counter 122 or from the input of the burstinterrupt signal.

The block ES 118, as shown in FIG. 12, has a configuration, for example,as shown in FIG. 14. Clocked inverters 131 operate as inverters when theEND signal and the /END signal rise, and when these signals END and /ENDfall, the output of the clocked inverters 131 becomes a high impedance.The /END signal is complementary to the END signal, therefore wheneverthe END signal is in pulse form, the signals R1 and R2 rise alternatelyas shown in FIG. 15.

In this manner, in the second embodiment described above, by providingtwo internal clock systems 1 and 2 for controlling the burst datatransfer and using these two systems 1 and 2 alternately, it is possibleto eliminate restrictions on the burst data transfer because of the timerequired to reset the clock system. In addition, by combining the secondembodiment with the first embodiment having the architecturalconfiguration shown in FIG. 6, the area required in the system can bereduced and therefore the cost is reduced. It is therefore possible toprovide a large volume SDRAM combined with the advantage of mitigatingthe restrictions relating to burst data transfer.

As explained in the foregoing, in the present invention, the banks aredivided into a plurality of blocks, the I/O buses are divided tocorrespond to the various blocks, the I/O buses are used in commonbetween adjacent banks, and the data buses are also used in commonbetween adjacent cell arrays. It is therefore possible to optimize thelayout configuration of the cell array and the mechanism of a burst datatransfer and to achieve a size reduction of a synchronous DRAM.

In addition, two control systems for controlling the burst data transferare provided by the present invention, therefore by using the twosystems alternately, a reduction in transmission speed is prevented byresetting the burst data burst transfer, and it is possible to achievehigh speed data burst transmissions.

While the above provides a full and complete disclosure of the preferredembodiments of the present invention, various modifications, alternateconstructions and equivalents any be employed without departing from thetrue spirit and scope of the invention. Therefore the above descriptionand illustration should not be construed as limiting the scope of theinvention, which is defined by the appended claims.

What is claimed is:
 1. A synchronous DRAM comprising:a plurality ofmemory cell arrays each having a plurality of memory cells arranged in amatrix, each of the memory cell arrays having a plurality of bit linepairs arranged in a column direction; a plurality of sense amplifierarrays each inserted between two of the memory cell arrays, each of thesense amplifier arrays having a plurality of sense amplifier circuitsarranged in a row direction, with the sense amplifier circuits beingcoupled to the bit line pairs; a plurality of row decoder circuits,wherein a row decoder circuit is provided for each of the memory cellarrays for selecting the memory cells in one row; a plurality of senseamplifier activation circuits, wherein a sense amplifier activationcircuit is provided for each of the sense amplifier arrays foractivating the sense amplifier circuits corresponding to a selectedsense amplifier array; a circuit for receiving address signals and forselecting at least two of the row decoder circuits and at least four ofthe sense amplifier activation circuits in a single access operation; aplurality of first data buses each inserted between two of the memorycell arrays, each of the first data buses having a plurality of firstdata line pairs arranged in the row direction; a second data bus havinga plurality of second data line pairs arranged in the column direction;and a plurality of data line selection circuits, one of the plurality ofdata line selection circuits provided for each of the first data buses,the data line selection circuits for selectively connecting one pairfrom the first data line pairs to one pair from the second data linepairs.